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This class hides and serves as a substitute for the underlying logging
system's MDC implementation.

If the underlying logging system offers MDC functionality, then SLF4J's MDC,
i.e. this class, will delegate to the underlying system's MDC. Note that at
this time, only two logging systems, namely log4j and logback, offer MDC
functionality. For java.util.logging which does not support MDC,
org.slf4j.helpers.BasicMDCAdapter will be used. For other systems, i.e slf4j-simple
and slf4j-nop, org.slf4j.helpers.NOPMDCAdapter will be used.

Thus, as a SLF4J user, you can take advantage of MDC in the presence of log4j,
logback, or java.util.logging, but without forcing these systems as
dependencies upon your users.

For more information on MDC please see the chapter on MDC in the
logback manual.

Put a diagnostic context value (the val parameter) as identified with the
key parameter into the current thread's diagnostic context map. The
key parameter cannot be null. The val parameter
can be null only if the underlying implementation supports it.

This method delegates all work to the MDC of the underlying logging system.

Remove the diagnostic context identified by the key parameter using
the underlying system's MDC implementation. The key parameter
cannot be null. This method does nothing if there is no previous value
associated with key.

Set the current thread's context map by first clearing any existing map and
then copying the map passed as parameter. The context map passed as
parameter must only contain keys and values of type String.